Monday, 29 August 2016

So got a bit of time to launch this rocket. I built it ages ago (it's an Estes Star Stryker kit albeit with an adapted 3dprinted nose) as I wanted to build the smallest payload carrying model rocket and indeed build a diy altimeter to go in it.

So the launch and recovery went really well, low wind and clear skies I fired it with a B6-4 motor as I quite wanted to get it back! It launched straight and stable, deployed the chute well and was easily recovered (avoided trees).. perfect.

The DIY altimeter (think I'm calling it SIMPalt) seems fine after a reasonable quick decent (I think the 13 gram weight is at the limit of what the star stryker is probably designed to cope with payload wise). I was primarily interested in whether the SIMPalt hardware would hold together structurally rather than the data as the code for the altimeter is primitive (library based and not calibrated) and at some point will be replaced with some code a much more talented buddy is working on for me.

However.. just for fun I pulled the data from the SD card and made a quick curve.. this should not be taken as accurate (can't remember how fast this code was managing SD writes on the logic analyser etc...) but I am quite pleased that despite the noise the shape of the curve is pretty representative of the flight, the apogee to chute deploy and then the change in gradient as it's descent is slowed by the chute particularly.

Tuesday, 16 August 2016

Finished making a little case (well a front and a back!) for this variable power supply that I had worked out and wired up a while back and then had on the (enormous) to do pile! I finally got round to drawing a bit of cad and I cnc routed these panels. The panels are just 4mm mdf with a bit of spraypaint to finish them. The gubbins comprises of a very cheap variable voltage dc-dc board which is a lm2596. They come with a small ceramic pot on the board to vary the voltage but I've replaced that eventually with a 10 turn pot to give me the resolution I need to set the voltage to 2 decimal places! (I say eventually, in testing I used an ordinary pot which proved the concept but was difficult to even hit a value to the nearest volt!!)

These variable buck dc-dc boards take a voltage input of anything between 4v and 35v and will output a voltage range between 1.23-30v, they seem pretty stable. The display is a 3 digit voltage display like THIS, It is important you get one that is listed as having 3 wires, namely then it takes its power supply from the input voltage and has a third wire connected to measure the output voltage.. there are some that only have 2 wires that just connect across the output voltage which means when the voltage drops below around 3.3v.... they turn off! The 3 wire ones happy measure down to the minimum values. (note neither of the links are traders I've used.. rather just to show the stuff!)

The back panel has the inputs on the right and the outputs on the left all on 4mm banana jacks... I love cnc routing.. it makes you able to get these things really precise.. If I had had to drill those holes manually I would have designed it with more space between them making the entire thing bigger!

Thursday, 11 August 2016

So.. Been on holiday and toured around Europe taking in 9 countries and doing about 2600 miles over 3 weeks.. lovely! One highlight that is geeky enough to warrant a blogpost is I got a quick trip in to CERN just north of Geneva. As I had the kids with me the 4 hour tour was out of the question but the 2 visitors centres (mikrocosmos and the Innovation Sphere) where definitely do able... and they were brilliant. One of my best parts was chatting to an amazing guide ( a particle physicist who did shifts in the visitors centre and was FULL of passion) and in particular we talked about CERN and open source, prompted by me mentioning using Kicad which CERN have used and developed and shared back into the community, he spoke at length about numerous complex high end software/systems that CERN has done this with and affirmed in me that across the vast majority of the huge complex that is CERN and LHC and ALICE and ATLAS and CMS an open source attitude prevailed. It was reaffirmed later in the trip wen you stand in front of a console that shows in realtime the data flow mapped over the world that is CONSTANTLY being streamed to hundreds of recipients around the world. Inspiring... I used to alway say that the ISS is mankinds greatest technological achievement... but darn... CERN is a close call...